Digital Cement Integrity: A Methodology for 3D Visualization of Cracks and Microannuli in Well Cement

Abstract

Leakages of greenhouse gases, such as methane and carbon dioxide from wells, may have considerable environmental consequences. Although much emphasis is currently put on understanding well barrier failures, and thus, preventing well leakages, especially for an important barrier material as cement, there are still several knowledge gaps and unknowns. However, a step-change in well integrity understanding may be obtained by applying advanced characterization techniques and scientific approaches to studying well barrier materials and their failure mechanisms. This paper describes the development of an experimental methodology that uses X-ray computed tomography to obtain 3D visualizations of cracks and microannuli in annular cement sheaths. Several results are included that demonstrate the value of using such digital methods to study well cement, and it is shown that such experimental studies provide an improved understanding of cement sheath integrity. For example, it is seen that radial cracks do not form in symmetrical patterns and that microannuli do not have uniform geometries. Such experimental findings can potentially be used as benchmark to validate and improve cement integrity simulation tools.

Assessment of Cementitious Composites for High-Temperature Geothermal Wells

“…The procedure was continued, with a 1 MPa increase in pressure at each step, until a complete failure of the sample was observed. A detailed description of the procedure and the following analysis can be found in [ 41 ].…”

Squeeze cementing of micro-annuli: A visco-plastic invasion flow

“…These experiments are typically conducted on scaled-down sections of wells and aim to recreate downhole conditions such as temperature and pressure cycling. Computer tomography (CT) has been used to determine the size of leakage pathways [10][11][12][13], showing that microannulus geometries are highly variable in nature. A complex network of pathways with non-uniform thickness were observed in their samples with connectivity of pathways in the axial direction.…”

Impact of microannulus on the efficiency of heat transfer in the bottomhole

“…In extreme cases, the microannulus encompasses the full circumference of the wellbore. However, in most cases, only part or the cement is affected, as it can be seen in cement evaluation logs (Vrålstad and Skorpa, 2020;Santos and Dahi Taleghani, 2021). To evaluate the effect of the size of the microannulus on the bottomhole temperature, different degrees of severity were evaluated, ranging from 0 (no microannulus) to 1 (full circumference).…”